Fayum mummy portraits.
"An Egyptian mummy that was decorated with a woman's portrait contained a surprise — the body of a child who was only 5 years old when she died. Now, scientists have learned more about the mysterious girl and her burial, thanks to high-resolution scans and X-ray 'microbeams' that targeted very small regions in the intact artifact." Source: Live Science.
Note: This is Hawara Portrait Mummy No. 4, one of the famous Fayum portrait mummies (I think). The fact that this is a child's mummy has apparently been known for some time. For instance, a paper which appeared in the 1985 Journal of Egyptian Archaeology states that "its small size indicates that this is the mummy of a child."
When the mummy was examined, "a small, elliptical object" was discovered in the wrappings over the abdomen:
"X-ray diffraction showed that it was made of calcite — but what was it? One possibility is that it could be an amulet included because the child's body was damaged during mummification ... After such a mishap, priests would often place an amulet such as a scarab over the damaged body part to protect the person in the afterlife, and the newfound calcite 'blob' was about the right size and in the right position for it to be a protective scarab..."